Independent Technical Review of Winthrop Shores Reservation Restoration Project
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INDEPENDENT TECHNICAL REVIEW OF WINTHROP SHORES RESERVATION RESTORATION PROJECT EXECUTIVE SUMMARY Over the last three years, the DCR has implemented long‐delayed improvements to Winthrop Beach that were first proposed in the 1993 “Back to the Beaches Plan.” The highly eroded beach required rebuilding to protect the seawall and reduce flooding and damage to the adjacent neighborhood of five thousand people. Work completed from 2013‐2014 included placement of approximately 500,000 cubic yards of material on the beach, repairs to existing groins and construction of a new terminal groin at the northerly end of the beach. While the completed project has, thus far, fulfilled its role as shore protection, wave and tidal action has washed away fine sediments from the seaward edge of the northerly portion of the beach, leaving steep ridges of loose rounded stone and cobbles which are very difficult to traverse on foot, impairing public access. DCR contracted with Tetra Tech, Inc. to review and evaluate the design and construction of the project in terms of best coastal engineering practices. Tetra Tech’s findings are as follows: 1. The studies and design reports leading to the final design were competently performed, using standard coastal engineering design principles as well as competent, adequately performed numerical modeling simulations of anticipated Project performance. Further, the inputs to those models were all in the range of acceptable scientific and engineering judgement. 2. The contract documents for the southern sections, DCR Project P11‐2686‐C3A and northern section, DCR Project P11‐2686‐C4A are competently prepared, meet the applicable engineering standards for such coastal workd an reflect the results of the design studies. 3. The Project reflects the beach nourishment effectiveness for Shore Protection and Flood Damage Reduction conclusions reached by the U.S. Army Corps of Engineers in their August 1994 Reconnaissance Report for Winthrop Beach. 4. The Project as built and in today’s post‐construction condition provides a significant improvement to shore protection from pre‐construction conditions. 1 of 27 5. The use of the soils from the Saugus roadway embankment mixed with gravel and cobble, from quarries in Lancaster and Carver, MA provided suitable and appropriately sized materials for beach nourishment on Winthrop Beach. 6. Given Winthrop Beach’s open‐ocean exposure to the most damaging NE‐ENE winds, the depth of the Broad Sound near shore and the high‐energy waves which result from that setting, it is not reasonably possible to maintain the nourishment as a sandy beach over the entire Project length. 7. In large measure, the eroded nourishment materials are not “lost” ‐ nor has the fill been wasted; rather: the sediments have been resorted and redistributed by nature, with the shingle, cobble components redistributed by waves and tidal forces into tall, steep shingle berms in the exposed areas; the sand components have been washed into the broad sandy high‐tide salient (curved beach) in the wave shadow of Five Sisters; and, a gravelly, coarse sand low‐tide beach is present between the salient and the breakwaters. TECHNICAL REVIEW The following is Tetra Tech’s report on its review of the Winthrop Beach Nourishment Project (also referred to, variously, as the Winthrop Shores Reservation Restoration Project and the Winthrop Shore Protection Design Project; for simplicity, hereafter the “Project”). Responses to questions posed to the Massachusetts Department of Conservation and Recreation (DCR), observations during a site visit conducted by two members of the Tetra Tech Team on 05 May 2016, relevant clarifications provided in a teleconference call held between representatives of DCR, the Parsons Brinckerhoff Team and Tetra Tech on 05 May, and an on‐site meeting with DCR staff on 06 May all serve to contribute to the findings of this report. 1. BACKGROUND In response to Winthrop residents’ displeasure with the stony composition of the seaward face of the completed Project, the Massachusetts Department of Conservation and Recreation (DCR) retained Tetra Tech Inc. to provide an independent technical review to determine if this shore protection project was designed and constructed in accordance with best engineering practices. The effort includes a review of relevant Project documents, discussions with DCR staff and site visit observations conducted on 05 and 06 May 2016. The overall Project location (within which the approximate limits of restoration – constructed in two segments and referenced as ‘southern nourishment’ of 960 feet [ft] and a ‘northern nourishment’ segment of 2,200 ft) is shown in Figure 1. The Project documents that were provided to Tetra Tech for review are 2 of 27 listed in routing slips from DCR dated 22 March 2016 and 28 April 2016 and included as Appendix A. In addition, DCR provided responses to questions posed by Tetra Tech; these responses are provided as Appendix B. 2. PREVIOUS STUDIES In the early 1970s, the Metropolitan District Commission (now DCR) retained Dr. Miles Hayes of the University of South Carolina to review the coastal geologic conditions of the Boston coastal segments within Broad Sound and to provide recommendations for their restoration as beach areas. Dr. Hayes’ final report1 includes descriptions of the three beach areas, causes of beach erosion, and recommendations for the restoration of the beaches of Revere, Winthrop and Nantasket. The listed causes of erosion are: 1. Natural depletion of the sources of sediment; 2. Removal of sediment by man; 3. Reflection of waves off of vertical seawalls; 4. Abolition of dune areas; and, 5. Focusing of waves by refraction off of offshore bottom features. Figure 1. Winthrop Shores Reservation Restoration Program – Shore Protection Project Limits (image courtesy of Google Earth) 1 Hayes, M., O., E. K. Hubbard and D. M. FitzGerald (1973). Investigation of Beach Erosion Problems at Revere, Winthrop and Nantasket Beaches, Massachusetts, Department of Geology, University of South Carolina, Columbia, SC. 3 of 27 The second and third listed causes are currently (May 2016) under effective control in the Project boundaries, as a result of the constructed Project. However, the remaining three causes are still active in influencing erosion. The Hayes report emphasizes the importance of wave energy focusing by refraction on erosion at Winthrop Beach. The effect is so strong that the Hayes report goes on to recommend that: “Emplacement of sand fill at Winthrop Beach would be a waste of resources inasmuch as it will not stay on that beach because of the steep offshore slope, the exposure to large waves, and the difficulty in providing enough sand to avoid wave reflection from the seawall.”2 The report went on to recommend the placement of riprap or coarse gravel on the beach as a means to protect the seawall. It is noted that, as a component of the constructed Project, a significant portion of the northern nourishment (72,392 cubic yards of the 367,718 cubic yards of material placed) was quarry‐sourced/delivered gravel and cobble‐sized sediments. The Hayes report did provide recommendations for beach nourishment at Revere and Nantasket Beaches. Anecdotal mentions of the (at the time of preparation of the report) ‘recent’ Revere beach nourishment project suggested that it was performing up to public expectations. The Hayes report further recommends the discontinuation of certain beach manicuring practices that have been used over the years at all three of the beaches studied. These include: Removal of stone and gravel from the beach; Bulldozing the natural beach profile into a plane surface; Pushing of gravel off of the berm (horizontal plateau formed by the deposition of beach material by wave action) and into the intertidal zone; and, Pushing sand from the intertidal zone onto the berm.3 It is noted that, while the above recommendations have merit from a coastal processes standpoint, there does not appear to be consideration given toward public safety or the ability of the public to gain reasonable access to the intertidal beach/shoreline. In the lee (shadow) of the Winthrop Beach breakwaters, there appears to be sand remaining in the system, as evidenced during low tide. In this shadow region, there is no need for regrading activities. It is possible that this shoreline segment could realize sand transport back onto the upper portions of the berm under less energetic wave conditions typically associated withe lat spring/summer. At the specific request of the Massachusetts Metropolitan District Commission (MDC‐ predecessor agency to the DCR), the U.S. Army Corps of Engineers completed a study4 of the 2 Ibid, page 6. 3 Ibid, page 5. 4 of 27 Project area. The MDC sought federal participation and funding for the protection of the seawall and adjacent roadway and utilities following the no‐name storm of October 1991 and the December 1992 blizzard. The 1994 Reconnaissance Report considered a variety of shore protection options including modifications to the existing seawall and groins; revetment placement; construction of additional breakwaters; and beach restoration and nourishment. The report states “the most supportable alternative would appear to be placement of beachfill material.”5 In the late 1990’s, the DCR retained the design team led by Parsons Brinckerhoff with coastal engineering support from Aubrey Consulting/Woods Hole Group, Inc. and Applied Coastal Research & Engineering, Inc. The proposed restoration project designed by the Parsons Brinckerhoff team was consistent with the earlier reconnaissance study recommendations of the U.S. Army Corps of Engineers. 3. RESTORATION PROJECT FIELD STUDIES Field investigation programs are outlined in some of the reviewed reports6 and 7. The reports cover: waves; water levels; winds; shoreline changes; sediment characteristics; condition of beach and beach amenities; inventory and description of sand trapping structures; and environmental, wetland and water quality issues. The studies appear to be comprehensive in nature and with a scope appropriate to the design of the restoration project.